Molds, such as those used in injection molding, typically include two mold halves that can each be equipped with a mold cavity used to make some part. During molding, relative movement between the mold halves bring the two halves together to initiate a molding cycle. A moldable material, such as a plastic, a resin, or the like, is injected into each cavity. After the moldable material has had a certain amount of time to set, the mold halves are separated and the molded part is ejected.
This process typically does not take very long. For example, in some molding application, the complete cycle time to make a molded component can be as little as a couple of seconds.
Molds are equipped with mold interlocks that help ensure accurate alignment and guidance of the mold halves during mold setup and later when they are repeatedly being brought together during operation. Such locks are also intended to help ensure guidance between mold cores and stripper inserts, when such mold components are used.
Typically, each mold has four such interlocks with an interlock located along each side of the mold. Each interlock includes a head, or male portion, that is attached to one mold half and a receptacle, or female portion, that is attached to the other mold half. When the mold halves come together, the head of each interlock is received in its respective receptacle helping to ensure accurate mating of the mold halves.
During mold setup, interlocks are attached to the mold halves at parting line and one mold half is brought into mating contact with the other mold half. When mated, the head of each interlock is received in its respective receptacle. Various components of the mold are thereafter adjusted to locate the mated mold halves relative to each other. This helps ensure smooth, fast and accurate operation of the mold during molding operation.
During molding operation, as the mold halves are brought together, the head of each interlock is received in the receptacle. The receptacle has one or more sidewalls that guide movement of the head as it enters and moves into the receptacle. As the head enters and moves into the receptacle it helps guide the mold halves together to ensure that that they accurately mate with each other. By helping to ensure accurate mating, mold interlocks help correct or compensate for slight misalignment between mold halves. This also helps ensure that mold cavities accurately overlie each other during molding and that the mold cavity shut-offs properly align.
One very common type of mold interlock is a side lock. A side lock has a head that extends outwardly from a horizontal mounting base that is of square or rectangular cross section. The head is defined by straight sidewalls that are typically generally perpendicular to the base. During operation, the head is received in a receptacle that is defined by a pair of straight sidewalls that are generally parallel to the straight sidewalls of the head.
Side locks are simple to use and install. They typically designed with an angular clearance of zero degrees and a dimensional clearance of between 0.0002 and 0.0004 inch between the head and the receptacle. They also allow for thermal expansion of the mold halves when properly installed. Zero clearance locking fitting typically is not required.
They are not without drawbacks. Their relatively narrow clearance means that they can bind if not opened in parallel, which can occur if there is some misalignment. These types of locks give little protection to smaller angle shut-offs, which can lead to close-off or shut-off misalignment or clashing. They usually need lubrication, which means that they cannot be used in certain medical and food component molding applications where lubricants typically cannot be used. Even when lubricated, metal to metal contact between the head and receptacle often result in excessive wear because any lubricant is often wiped during mold operation.
Another common type of lock is a rectangular tapered interlock. They are similar in construction to a side lock, except that its head is longer and its sidewalls tapered. While its sidewalls that define its head are straight, each sidewall has a taper angle of about 10° from perpendicular. Each sidewall of the receptacle in which the head is received is complementarily tapered. This type of lock is machined into both cavity mold halves at parting line and adjusted to zero clearance by grinding the overall height of the head.
This type of mold interlock is easy to install, provides a larger contact area, and accommodates greater mold misalignment than does a side lock. However, it too suffers from many of the drawbacks of side locks. For example, its tapered straight sidewall construction provides little protection to relatively small angle shut-offs. As a result, shut-off misalignment or clashing can undesirably occur. Lubrication can also be a problem. This can limit its use and lead to premature replacement due to excessive wear.
A still further type of mold interlock is a tapered round interlock. It has a head defined by a tapered, conical sidewall that is received in a complementary receptacle. Its application is limited because it does not accommodate thermal expansion and provide little protection for smaller angle shut-offs.
What is needed is a mold interlock that does not suffer from at least one or more of the aforementioned drawbacks. What is also needed is a mold interlock that is more economical to use.